This invention relates to processes for the preparation of diphenylmethanes including diphenylmethane and alkyl-substituted diphenylmethanes.
Diphenylmethanes are useful intermediates in the preparation of anthraquinone, anthracene and other fused ring compounds. The diphenylmethanes have been prepared by the reaction of chloro-methylbenzenes, e.g., benzyl chloride, with benzene or substituted benzenes such as toluene in the presence of a dehydrohalogenation catalyst such as aluminum chloride, copper chromite, hydrofluoric acid and sulfuric acid. See, for example, U.S. Pat. Nos. 4,117,019; 4,339,621 and 4,304,949. Unfortunately, most of such processes yield unwanted by-products which are difficult to separate from the desired diphenylmethanes. Processes employing sulfuric acid or similar liquid acid catalyst yield a liquid product mixture wherein it is expensive to separate the desired diphenylmethane from the catalyst and other components of the product mixture. Furthermore, when sulfuric acid is used as the catalyst, it is often necessary to employ a substantial excess of the benzene reactant in order to inhibit unwanted sulfonation of the resultant product.
In view of the deficiencies of the aforementioned prior art processes, it is highly desirable to provide a new process for making diphenylmethanes in a product mixture from which the diphenylmethanes can be separated in high yield and high purity using simple distillation.